Apparatus for defrosting cooling units of absorption refrigeration systems

ABSTRACT

This invention relates to an absorption refrigeration system of the inert gas type including cooling structure having low and higher temperature cooling elements to which refrigerant is supplied from a vapor expulsion unit having a heat receiving part from which heat is derived for expelling refrigerant vapor from absorption liquid. The vapor expulsion unit includes a first pump for lifting liquid by vapor-liquid lift action to effect normal circulation of absorption liquid during operation of the system. The heat receiving part is heated by a source of heat controlled by a thermostat affected by the temperature of the higher temperature cooling element either to render said first pump operable to circulate absorption liquid or to render it inoperable to stop circulation of the liquid. The absorption liquid circuit has a part at a level normally free of liquid and above the liquid surface level therein when normal circulation of liquid is effected and at a level below the liquid surface level in the circuit when normal circulation of liquid has stopped. The important feature of the invention resides in providing a second pump for lifting liquid by vapor-liquid lift action by heat which also is derived from the heat receiving part and is connected to the one part to receive liquid therefrom when circulation of absorption liquid has stopped. Fluid raised by the second pump is conducted to the higher temperature cooling element to melt frost which tends to form thereon.

United States Patent [72] Inventor Wilhelm Georg Kogel PrimaryExaminer-Martin P. Schwadron Stockholm, Sweden Assistant ExaminerP. D.Ferguson [2]] Appl. No. 776,535 Attorney-Edmund A. Fenander [22] FiledNov. 18, 1968 [45] Patented May 25, 1971 73 Assignee Akti b l t El t lABSTRACT: This invention relates to an absorption refrigera- Stockholm,Sweden tion system of the inert gas type including cooling structure[32] Priority Nov. 17, 1967 having low and higher temperature coolingelements to which [33] Sweden refrigerant is supplied from a vaporexpulsion unit having a [3 l] 15818/67 heat receiving part from whichheat is derived for expelling refrigerant vapor from absorption liquid.The vapor expulsion unit includes a first pump for lifting liquid byvapor-liquid lift action to effect normal circulation of absorptionliquid during operation of the system. The heat receiving part is heatedby a [54] APPARATUS FOR DEFROSTING COOLING UNlTS source of lies}:cplntlzolled by a thermostat affected by the tem- OF ABSORPTIONREFRIGERATION SYSTEMS pet-Store o! it e 1g er tempebrlature coolingelement either to 6 Claims, 6 Drawing Figs ren er sat rst pump opera eto circulate absorption llqllld or to render it inoperable to stopcirculation of the liquid. The [52] US. Cl 62/148, absorpdon liquidcircuit has a part at a level normally f f 62/151-52/277162/49Q62/493liquid and above the liquid surface level therein when normal [51] Int.Cl F25b 15/10 circulation fli id is ff t d and at a level below theliquid [50] Field of Search 62/81, 476, Surface level in the circuitwhen normal circulation f liquid 497, 277 has stopped. The importantfeature of the invention resides in providing a second pump for liftingliquid by vapor-liquid lift [56] References cued action by heat whichalso is derived from the heat receiving UNITED STATES PATENTS part andis connected to the one part to receive liquid 2,881,598 4/ 1959Hellstrom 62/490X therefrom when circulation of absorption liquid hasstopped. 2,402,413 6/ 1946 Kogel 62/81 Fluid raised by the second pumpis conducted to the higher 3,163,997 1/ 1965 Stierlin 62/81 temperaturecooling element to melt frost which tends to form 3,277,665 10/1966Batson 62/227 thereon.

24 23 x n 8 f= 28 t 3! J\ 16 a I /7 /\J r 1 27 7 /4 I /.?0 /8" :1 /0 f i1 ll Patented May 25, 1971 4 Sheets-Sheet 1 Patented May 25, 1971 4Sheets-Sheet 2 TO CONDENSER TO CONDENSER Patented May 25, 1971 3,580,004

4 Sheets-Sheet 5 T0 CONDENSER Patented May 25, 1971 3,580,004

4 Sheets-Sheet 4 TO CONDENS\ APPARATUS FOR DEFROSTING COOLING UNITS OFABSORPTION REFRHGERATION SYSTEMS The present invention relates toapparatus for achieving defrosting in an absorption refrigeratingapparatus operation with inert and having a thermosiphon pump whichpraises fluid from the absorption liquid circuit to the evaporatorsystem.

It has already been proposed for defrosting purposes to pump warmabsorption solution from the boiler system to the evaporator system, forinstance by a pump with an independent heat source which is manually putinto action when it is desired to remove frost from an evaporator part.Other proposals for solving the problem mention a pump which is suppliedwith heat from the ordinary heat source of the apparatus but whichnormally does not contain liquid in the system. Instead, by some manualmeasure, the pump is supplied with a quantity of liquid at suchoccasions when defrosting is desired. Such arrangements do not operateautomatically and are comparatively expensive and not very reliable.They also have some other deficiencies, such as the circumstance thatrelatively great quantities of frost may be accumulated before there isan opportunity of defrosting, which unfavorably affects the operation ofthe apparatus.

Another solution of the problem having great advantages has been used inpractice. According to this solution, the apparatus is provided with aconnecting conduit between the vapor space of the boiler system and theevaporator system, part of the conduit having the shape of a U-pipe.Thus, it is known to let vapors coming from the boiler system condensein a container and be collected there as condensate starting at acertain level so as to form a liquid seal when the condensate has risento a higher level, the liquid seal then cutting off the connection tothe evaporator system. When the liquid has risen to a certain levelsituated over the liquid seal, a siphon is put into action whereby theliquid column built up will be removed and a free passage be obtainedbetween the vapor space of the boiler and the evaporator system. Theknown apparatus is so adjusted that a relatively long time elapsesbetween defrosting periods which have such duration and effectivity thatfrost on the evaporator is removed even under difficult conditions.However, the length of the defrosting time is the same under easierconditions which should not be necessary.

The present invention has for its purpose to provide apparatus fordefrosting in shorter periods following close to each other and,particularly, being to some extent adapted to the need of defrosting.Further, it is an object of the invention to provide an improveddefrosting arrangement by simple and cheap but reliable means. Theintended purpose is achieved according to the invention mainly therebythat apump other than the absorption liquid circulation pump is suppliedwith absorption solution intermittently and automatically and operatedby the heat receiving part of the boiler system of the apparatus fromwhich heat is derived to effect operation of the apparatus.

The invention will be further described hereinafter with reference tosome embodiments shown schematically in the attached drawings and chosenby way of example, in which connection also other characteristics of theinvention and features thereof will appear. FIG 1 illustrates anabsorption refrigerating apparatus embodying the invention whichoperates with inert gas and is provided with an analyzer, FIGS. 2 to 4are fragmentary views of the refrigerating apparatus shown in FIG. I toillustrate other embodiments of the invention; FIG. 4a is a fragmentarysectional view taken at line 40-441 of FIG. 4, and FIG. 5 is anotherfragmentary view of the refrigeration apparatus illustrated in FIG. lwhich shows the invention used in an absorption refrigerating apparatuswithout an analyzer.

FIG. 1 shows mainly schematically an absorption refrigerating apparatuswhich is well known but which is furthermore provided with a means fordefrosting according to the invention. The refrigerating apparatus canoperate with ammonia as refrigerant, water as absorption medium andhydrogen as inert gas. Absorption solution rich in refrigerant passesfrom the absorber vessel through the outer conduit of the liquid heatexchanger 11. The rich solution from an end of the liquid heat 5exchanger is supplied to the liquid circulation pump 12 of theapparatus, the pump with its suction side 13 being connected to thelower part of the heat exchanger. The pump 12 is heat conductivelyconnected to a sleeve 14 which functions as a heat receiving part and inwhich an electric heating cartridge 9 is placed. This sleeve can also bereplaced by a flue for a burner operable by gas or kerosene. The richsolution is pumped up to a standpipe 15 from which the weak absorptionsolution is conducted through the inner conduit of the liquid heatexchanger 11 and a conduit 16 and flows over into the upper part of theabsorber 17. The weak solution flows down through the absorber 17 incountercurrent to inert gas rich in refrigerant and coming from theevaporator system and which washed out of refrigerant, whereafter therich solution is collected in the absorber vessel 10. The liquid heatexchanger 11 has an essentially horizontal portion 18 placed at acomparatively high level which is situated lower (about 25 mm.) than theliquid level I which, on account of the level of the heat conductiveconnection between the pump 12 and the sleeve 14, is normal for theliquid in the absorber vessel 10 when the apparatus is in operation. I

The ammonia vapors generated in the pump 12 are separated in thestandpipe 15 from the lifted solution and pass through a vapor conduit19 which discharges into the horizontal portion 18 of the liquid heatexchanger where the vapor bubbles through the rich solution which flowsfrom the absorber vessel 10 and is somewhat preheated in the liquid heatexchanger 11. Thereafter, the vapor is conducted through a vapor conduit20 to a rectifier or water separator 21 and a condenser 22. Therefrigerant is condensed in the condenser 22 and then flows through aconduit 23 into a low temperature part 24 of the evaporator system wherethe refrigerant is again evaporated into weak inert gas flowing from thegas heat exchanger 25 of the apparatus. The gas mixture and unevaporatedliquid refrigerant flow down into a high temperature part 26 of theevaporator system where further evaporation takes place before the gasmixture is conducted into the gas heat exchanger 25 and a conduit 27 tothe absorber vessel 10. To equalize the pressure between the condenserpart and the absorber system, a conduit 28 is arranged because theconnection between these parts through the conduit 23 is filled withliquid. The refrigeration system is controlled by a thermal bulb 8 whichis affected by a temperature condition of the higher temperatureevaporator part 26. The thermal bulb 8, which is arranged to beinfluenced by the temperature of air which is cooled by the highertemperature evaporator part 26, is connected by a conduit 7 to a controldevice 6 operatively associated with a switch 5 connected in one of theconductors 4 for supplying electrical energy to heating element 9.

In a manner well known in the art the thermal bulb 8 and conduit 7 formpart of an expansible fluid thermostat which is charged with a suitablevolatile fluid and responds to changes in a temperature conditionaffected by the higher temperature evaporator part 26 to operate controldevice 6 and the switch 5 operatively associated therewith to close andopen the switch with increase and decrease, respectively, of thetemperature of the air cooled by the higher temperature evaporator part26.

The apparatus thus far described operates in a well known manner.According to the invention it is, however, also provided with anarrangement for defrosting which will now be described.

A pipe 29 is connected to the vapor conduit 19 at a point 30' the pipe29 extends down from the lower end of the sleeve for a distance which islonger than the distance between the liquid level 1 in the absorbervessel and the level of the connection of the vapor conduit 19 to theliquid heat exchanger 11 at the horizontal portion 18 thereof. To thelower part of the pipe 29, the suction side of a second pump 31 isconnected. This pump discharges into the upper part of a pipe 32 whichis inclined downward and connected to the inlet to the high temperatureevaporator element 26 of the apparatus. The second pump 31 has an innerdiameter which is smaller than the diameter of pump 12 of the apparatuswhich is employed to circulate absorption liquid in its circuit. Withabout the same location and length as the heat conductive contactbetween the liquid circulation pump 12 and the sleeve 14, the secondpump 31 is arranged in heat conductive connection with the liquidcirculation pump 12.

When the apparatus is in normal operation, the liquid level in the pipe29 stands at a low point 33. In the second independent employed fordefrosting, the liquid is in direct connection with the low pressureside of the apparatus and extends up to a level 34 which is as muchhigher situated than the level 33 in the conduit 29 as the heightdifference between the liquid level 1 in the absorber vessel 10 and theinlet of the vapor pipe 19 to the liquid heat exchanger portion 18.Since the liquid levels 33 and 34 are situated under the heat source ofthe apparatus, the defrosting pump is out of action. Because the pump 31has a heat conductive connection to the heat source of the apparatus inthe sleeve 14 only by the intermediation of the circulation pump 12, thetemperature of the defrosting pump 31 will never exceed the temperatureof the circulation pump 12. In this way the risk of overheating andcorrosion in the defrosting pump 31, when not in operation, will beeliminated. An important feature of my invention is that the conduit 29forms a stationary component of the refrigeration system and provides apassageway for conducting liquid downward from the point or part 30 tothe pump 31 when the part 30 is below the liquid level ll in theabsorption liquid circuit which occurs when the normal circulation orabsorption liquid stops.

When the thermostat 6, 7, 8 of the apparatus opens switch anddisconnects the normal heat supply, the circulation pump 12 ceases tooperate after a few minutes. The flow from the absorber coil 17,however, continues some minutes more and, because the rest of the liquidcirculation has ceased, the liquid level in the absorber vessel and theconduits connected thereto will rise. 1n the vapor conduits 19 and 20,the liquid contents communicate through the outer conduit of the liquidheat exchanger 11 with the absorber vessel 10. Therefore, acorresponding rise of the liquid level will occur also in the twoconduits 19 and 20 up to the level 11. If the inlet of the conduit 29 atthe vapor conduit 19 is placed at a point 30, which is located below thelevel ll of the liquid in the absorber vessel 10 and in the vaporconduits 19, 20, when the apparatus is inoperative, the conduit 29 willbe filled with hot rich solution which also fills up the lower part ofthe pump conduit 31 to a corresponding level. When the thermostat thenext time closes the switch 5 and connects the heat source of theapparatus, the circulation pump 12 starts after a few minutes delay andbegins operating the liquid circulation. The vapors generated in thecirculation pump press down the liquid in the vapor pipe 19 to the inletof the portion 18 of the liquid heat exchanger and at the same time acorresponding depressing of liquid in the conduit 29 occurs. Thedefrosting pump 31, which is heat conductively connected to thecirculation pump 12, almost simultaneously with the circulation pumpreaches boiling temperature, whereby a mixture of vapor and liquid issupplied to the high temperature part 26 of the evaporator system anddefrosting is started. Since the defrosting pump 31 has a smallerdiameter than the circulation pump 12 and is connected to the lowpressure side of the apparatus, the defrosting pump will have a faststart when the heat source is connected.

The duration of the defrosting period is determined by the volume of theconduit 29 and by the point at the conduit 29 where the relation betweenoperation height and lifting height makes further pumping impossible. Inview of the fact that the conduit 29 is in heat conductive contact withthe sleeve 14, condensation of vapor from the vapor pipe 19 duringoperation of the apparatus is prevented and, therefore, the risk ofuncontrolled defrosting is eliminated. Because defrosting occurs atevery thermostat cut-in, defrosting for 2 to 3 minutes is sufficient tokeep the flanges 35 at the high temperature part 26 of the evaporatorsystem completely free of frost.

Boiler systems provided with an analyzer are subject to a pressuredifference between the parts which corresponds to the difference inheight between the liquid level I in the absorber vessel 10 and theinlet of the vapor conduit 19 to the conduit 18 of the liquid heatexchanger. If this difference in height is 30 mm. for example, theoverpressure in the vapor space of the boiler compared with other partsof the apparatus will be 30 mm. water column. This condition prevails aslong as the apparatus is in normal operation. lf the operation isinterrupted, for instance when the thermostat disconnects the heatsource, the temperature in the boiler system falls and therewith thepressure of the ammonia vapor also falls. Since there is no gasconnection between the vapor space of the boiler system and other partsof the apparatus, absorption solution is successively pressed up intothe parts of the boiler which formed the vapor space of the boiler asthe temperature in the boiler system falls. The solution, thus, ispressed up into the circulation pump 12, the standpipe 15 and the vaporconduit 19. lf the apparatus is shut off sufficiently long, the entireboiler system will be filled with liquid. The connection of the conduit29 to the vapor 19 therefore can be placed at a point which is locatedover the liquid level present in the vapor conduit 19 when the apparatusis not operating. This is a great advantage because the risk of theliquid from the conduit 19 unintentionally flowing down into the conduit29 is eliminated. ln absorption refrigerating apparatus provided with ananalyzer, the liquid columns in the vapor conduits 19 and 20 are subjectto certain fluctuations.

It is commonly known that frost deposits on the evaporator cause seriousproblems. If a long time is allowed to elapse between defrostings it mayoccur that such large quantities of frost and ice are formed on the hightemperature evaporator that the air circulation around this apparatuspart in the refrigerator cabinet is so heavily reduced tat thetemperatures in the cabinet itself will be too high in spite of the factthat the evaporator keeps the intended low temperature. This causes thethermostat to have to be adjusted to a higher step in order tocompensate for the impaired cabinet temperatures. In this way theoperation of the apparatus requires higher costs then would be requiredunder ideal conditions. It is clear that defrosting can be effectedmanually by disconnecting the refrigerating apparatus entirely but,then, the low temperature evaporator also is put out of operation whichis not at all desirable. When using the present invention a fastdefrosting at each thermostat cut-in occurs. Since this happenscomparatively often, there will not be time for much frost to accumulateand it is therefore sufficient with successive very short defrostingperiods. If the apparatus is operating under unfavorable. conditions,for instance at high ambient temperatures or high humidity in the air,the frost formation on the evaporator flanges 35 increases. Then thethermostat of the refrigerating apparatus has to be adjusted to a higherstep in order to maintain the intended cabinet temperature, whichresults in shorter cutoff periods. Therewith, also a greater number ofdefrostings per 24 hours is obtained, which under these more difficultoperating conditions is an advantage.

FIG. 2 illustrates another embodiment of how the invention which differsfrom the embodiment of FIG. 1 in that the connecting conduit 32 to thehigh temperature evaporator element 26 extends downward from theconnecting point 36 of the defrosting pump 31 to n. eonnectin g point 37of the standpipe 15. The point 37' is s tuated below the liquid level inthe standpipe 15 and, therefore, the lower part 37 of the connectingconduit 32 will contain weak absorption solution since it is incommunication with solution in the standpipe, The connecting point 36between the defrosting pump 31 and the connecting conduit 32 is situatedabove the liquid level in the part 37 of the connecting conduit. Thedefrosting pump 31 is supplied with rich solution from the liquidquantity which during the off-period of the apparatus has accumulated inthe pipe 29. The vapors generated in the defrosting pump 31 areconducted through the connecting conduit 32 to the high temperature part26 of the evaporator while the weak solution lifted in the defrostingpump 31 will flow into the standpipe through the conduit part 37 fromwhich this solution, together with weak solution from the circulationpump 12 will flow through the liquid heat exchanger and the conduit 16to the top of the absorber 17. In the arrangement of FIG. 2, thedefrosting effect will be smaller than in the embodiment of FIG. 1'provided they otherwise are similar. In FIG. 2 the absorption solutionlifted by the defrosting pump 31 will be useful for the apparatus in itsnormal operation.

Another embodiment of the invention is shown in FIG. 3. In FIG. 3 theconnection of the high temperature evaporator 26 to the defrosting pump31 comprises a U-shaped conduit 38, 39, the leg 38 of which is connectedto the high temperature evaporator and the leg 39 of which is connectedto the vapor conduit or leg 38 of the apparatus'at a point 40 which islocated somewhat higher than the connection of the connecting conduit 38to the high temperature evaporator 26. The defrosting pump 31 isconnected to the leg 39 of the connecting conduit at a point 39' whichis located above the liquid level in the 'conduit 39 and just below theconnecting point 40 of the leg 39 to the vapor conduit 20. A heatconductive metal sheet 41 connects the vapor conduit to the leg 39 inthe connecting conduit. The ammonia vapors generated in the defrostingpump 31 are conducted through the vapor conduit 20 to the rectifier orwater separator 21 and further on to the condenser, 22, as shown in FIG.1, where they, together with the vapors from the normal circulation pump12, are liquefied. The refrigerant condensate is conducted therefrom tothe evaporator system where the refrigeration process takes place. Theabsorption solution raised by the defrosting pump 31 is conductedthrough the connecting'conduit 39, 38 to the high temperature evaporator26 where the heat of the solution is used for defrosting. The conductivemetal sheet 41 functions to raise the temperature of the right hand leg39 of the connecting conduit during the on-period and thereby preventvapors from the vapor pipe 20 from condensing in this part of theconnecting conduit. In this way a certain defrosting effect in theevaporator part 26 can be effected and this effect can be varied bychanging the height of the liquid seal formed by liquid in the U-shapedconduit 38, 39 while at the same time the vapors lifted in thedefrosting pump 31 are used for the normal operation of the apparatus.

FIG. 4 illustrates another embodiment of the invention which differsfrom the embodiment of FIG. 3 in that the liquid to the defrosting pump31 is supplied from the absorber side instead of from the boiler side ofthe absorption liquid circuit. During periods of high load on therefrigerating apparatus or high ambient temperature, it is possible toaccumulate in a particular part of the absorber vessel rich solution byconduct ing to such part unevaporated refrigerant flowing from theevaporator. From such vessel the rich solution is again supplied to theabsorption liquid circuit when the operating conditions for theapparatus become less severe. If an apparatus is filled with relativelyrich solution, during the on-period a certain accumulation ofunevaporated refrigerant flowing from the evaporator always takes place.The concentration of refrigerant in that part of the absorber vesselwhich serves as an accumulating vessel will always be higher than therefrigerant concentration of the solution which drips down into theabsorber vessel from the absorber coil. These refrigerant concentrationconditions stated are valid particularly for the surface layers or theupper layers in the vessel parts.

In view of the foregoing, the absorber vessel 50 in FIG. 4 is divided bya partition wall 51 into a circulation vessel 52, to which rich solutionflows from the absorber 17 and an accumulating vessel 53, to whichunevaporated refrigerant from the evaporator system is introducedthrough the conduit 27. The refrigerant from the evaporator alsocontains a certain percentage of water which has accompanied the ammoniavapors from the boiler or vapor expulsion unit to the condenser 22.During normal operation, rich absorption solution flows from thecirculation vessel 52 through the outer conduit of the liquid heatexchanger 11 and the circulation pump 12 to the standpipe 15 in order toflow by gravity therefrom through the inner pipe of the liquid heatexchanger 11 and the conduit 16 to the top of the absorber 17. From theaccumulating vessel 53 which in its lower part communicates with thecirculation vessel 52 a conduit 54 leads, the connecting point of whichis located above the liquid level I which prevails in the circulationvessel 52 and the accumulating vessel 53 when the apparatus is inoperation. The other end of the conduit 54 extends into the boilerinsulation somewhat below the lower end of the sleeve 14. At this regionthe conduit 54 is connected to the defrosting pump 31 which has itsupper end connected to a connecting conduit 39; 38 to the hightemperature evaporator 26 in a manner similar to that shown in FIG. 3.

During the on-period of the apparatus the liquid level I in the vesselparts 52, 53 is below the connection of the conduit 54 to theaccumulating vessel 53. Since this vessel is supplied with very richliquid overflowing from the evaporator through the conduit 27, theliquid in the vessel part 53 is somewhat higher than in the other part52. During the main part of the on-period, the liquid level in theconduit 54 is located at a point 55 which lies just below the lowerlevel of the sleeve 14. When the thermostat opens the switch 5 anddisconnects the heat supply to the source of heat 9 of the apparatus,the liquid circulation of the apparatus ceases after one or two minutes.The afterflow of absorption solution from the absorber coil 17 raisesthe'liquid level in the absorber vessel 50. Since the vessel part 53 atits lower end communicates with the liquid in the vessel part 52, thelevel in both parts is raised. In FIG. 4 the liquid level in the vesselparts 52 and 53 during the on-period of the apparatus is located at theline I but rises after cessation of the liquid circulation to the levelII which is located higher than the connecting point for the conduit 54.Therefore, occasionally very rich solution is supplied into the conduit54. Before the thermostat cuts in the heat supply of the apparatus thenext time, the conduit 54 is completely filled with very rich solution.Also, very rich solution is present in the conduit 27 and in the vesselpart 53. One can count with an ammonia concentration of about 6070percent in the conduit 54 and in the upper part of the vessel part 53.In the circulation vessel 52, where the rich solution for the liquidcirculation ispresent, the ammonia concentration is about 3035 percent.Because the vessel part 53 communicates with the defrosting pump 31, avery rich solution is fed also into this pump. In the circulation pump12, which is in heat conductive connection with the sleeve 14, a liquidcolumn is present and has an ammonia concentration of about 30-35percent. In the defrosting pump 31, which is in heat conductiveconnection with the circulation pump 12,'a liquid column having aconcentration of about 6070 percent is present. If the working pressureof the refrigerating apparatus is for instance 25 kg./cm. boiling in thecirculation pump 12 is obtained at a temperature of about 150 C, whereasboiling can be obtained in the defrosting pump 31 already at atemperature of about C. When the thermostat cuts in the heat supply ofthe apparatus, the circulation pump 12 will supply heat and start thedefrosting pump 31 without itself starting to function immediately. Theammonia vapors generated in the defrosting pump 31 which are obtainedunder very favourable conditions, are supplied through the vapor pipe 20and the condenser 22, as shown in FIG. 1, to the low temperature.evaporator part 24. The solution lifted is, on the other hand, suppliedthrough the connecting conduit 39, 38 to the high temperature evaporator26 of the apparatus to effect defrosting. After a few minutes ofdefrosting, the operating height in the vertical part of the conduit 54will have decreased to such an extent that the pumping in the defrostingpump 31 ceases. The temperature now very rapidly increases in thecirculation pump 12 whereby the normal liquid circulation is started.

From the foregoing it will appear that different possibilities areavailable for supplying automatically a certain quantity of absorptionsolution to the independent thermosiphon pump 31 in the apparatus, whichsolution in the embodiment of FIG. 4 just described can very well bericher in refrigerant than the absorption solution conducted to theliquid circulation pump 12 of the apparatus. The quantity of liquidsupplied to the separate pump 31 at each occasion is in certaininstances larger than the quantity of solution required for the heattransport from the boiler system to the evaporator system. By measuresin the boiler system, one can in certain cases achieve a reduction ofthis heat transport (FIGS. 13) but it is also possible as willappearfrom FIGS. 2-4, in different ways to reduce the heat transfer to thehigh temperature evaporator 26 by measures taken on the working mediumlifted by the separate pump before this medium is supplied to the hightemperature evaporator. Thus, the quantity of working medium lifted bythe pump can be divided into vapor and solution and only vapor or onlyhot solution can be supplied to the evaporator part 26 and the rest beallowed to pass into another apparatus part. According to the embodimentin FIG. 2, the weak solution is conducted into the normal circulationcircuit and according to FIGS. 3 and 4, the ammonia vapor is conductedto the condenser. The heat quantities taken out of the boiler system orthrough the separate pump 31 for defrosting but not used for defrosting,thus do not form an extra source of losses but are instead used toperform useful work in the apparatus.

In the foregoing, the application of the invention has been described inconnection with an absorption refrigerating apparatus with an analyzerin the boiler system because such apparatus is suitable to show thatseveral different possibilities are at hand to use to advantage thelevel changes in the liquid circulation system between an operationaloperation condition and relaxing period of the apparatus. Such levelchanges occur, however, in absorption refrigerating apparatus in whichan analyzer is not employed. An embodiment of the invention in such arefrigerating apparatus is shown in FIG. in which the boiler systemcomprises a shell boiler. The boiler system in FIG. 5 is built around acentral pipe 60 in which an electric heating cartridge 9 can bearranged. The central pipe can also fonn a flue for a burner which canbe driven by gas or kerosene. A shell 61 surrounds the central pipe 60and forms the boiler of the apparatus. Inside the shell 61, whichcontains weak solution, the liquid circulation pump 62 of the apparatusis arranged. The pump 62 passes through the boiler 61 and is suppliedwith heat from the surrounding weak solution present in the shell. Richsolution from the absorber coil 63 flows down into the circulationvessel 64 and is thereafter conducted through the outer conduit 65 ofthe liquid heat exchanger to the liquid circulation pump 62. The weakand boiling solution in the shell 61 transfers heat to the richersolution in the pump pipe 62 whereby liquid and vapor are raised byvapor-liquid lift action to a standpipe 66 and raised liquid flows bygravity through the boiler shell 61, the inner pipe 67 of the liquidheat exchanger upward in a conduit 68 to the top of the absorber 63. Ina manner similar to that shown in FIG. 4, a part of the absorber vesselis made to form an accumulating vessel 69 for accumulation of very richsolution overflowing from the evaporator. A conduit 70 is connected tothe accumulating vessel 69 at a lever which is situated over the liquidlevel I present in the vessel when the apparatus is in normal operationand is connected to a separate pump 71 to effect defrosting. Thedefrosting pump 71 is by welding arranged in heat conductive connectionwith the boiler shell 61. The upper end of the pump 71 is connected by aconduit 72 to the high temperature evaporator 73. When the thermostatopens the switch 4 and disconnects the heat source 9 of therefrigerating apparatus, the liquid circulation of the apparatus ceasesafter I or 2 minutes. Then there is a certain after flow of absorptionsolution through the absorber coil 63, which raises the liquid level inthe circulation vessel 64 and the accumulating vessel 69 to the levelII, which is situated above the connecting point for the conduit 70 tothe accumulating vessel 69. In this way the conduits 70, 71 are filledwith very rich solution. When the thermostat next time connects the heatsource of the apparatus, boiling temperature is reached very fast insidethe shell boiler 61. This boiling temperature, however, is much higherthan the temperature required for pumping the very rich solution in theconduits 70 and 71 and, since the defrosting pump 61 is arranged in heatconductive connection with the shell of the boiler, the defrosting pumpwill very quickly supply the quantity of vapor and liquid required toeffect defrosting of the high temperature evaporator 73.

FIG. 5 only illustrates how the normal operation of the apparatus by thethermostat 6, 7, 8, can be used for supplying rich absorption liquid tothe separate pump 71 for transferring heat from the boiler system to theevaporator part 73. With such heat transfer it is possible to usemeasures like those described in the embodiments of FIGS. 2 to 4 inorder to reduce the heat quantity transferred to a value which will besuitable to effect defrosting without causing any extra heat losses tothe apparatus. As described above, it is possible to use part of theheat transferred by the separate pump to effect defrosting and use theremainder in the normal operation of the apparatus.

I claim:

1. An absorption refrigeration system of the inert gas type comprising:

a. a plurality of interconnected components;

b. an absorption liquid circuit comprising a plurality of saidcomponents including a vapor-expulsion unit with a heat receiving partfrom which heat is derived for expelling refrigerant vapor fromabsorption liquid;

c. a source of heat external to the system for heating said heatreceiving part;

C]. said vapor expulsion unit including a first pump for lifting liquidby vapor-liquid lift action to effect normal circulation of absorptionliquid in its circuit during operation of the system;

e. said components further including a condenser and cooling structurehaving low and higher temperature cooling elements;

f. first conduit means including said condenser for conductingrefrigerant fluid from said vapor-expulsion unit to said coolingstructure;

g. control means including a thermostat affected by the temperature ofsaid higher temperature cooling element for controlling said source ofheat to supply heat to said heat receiving part at a rate which willrender said first pump operable to raise liquid by vapor-liquid liftaction to normally circulate absorption liquid in its circuit duringoperation of the system or to substantially stop the supply of heat fromsaid heat source to said heat receiving part to render said first pumpsubstantially ineffective to raise liquid by vapor-liquid lift actionand substantially stop the normal circulation of absorption liquid inits circuit;

h. said absorption liquid circuit having at least one part at a levelwhich is normally free of liquid and above the liquid level therein whennormal circulation of absorption liquid is effected during operation ofthe system and below the liquid level in said circuit when the normalcirculation of absorption liquid has substantially stopped due to saidfirst pump being substantially ineffective to raise liquid byvapor-liquid lift action;

i. a second pump for lifting liquid by vapor-liquid lift action by heatderived from said heat receiving part;

j. second conduit means forming a stationary component of said systemand providing a passageway for conducting liquid downward from said onepart to said second pump when said one part is below the liquid level insaid absorption liquid circuit; and

k. third conduit means for conducting fluid from said second pump tosaid higher temperature cooling element.

2. An absorption refrigeration system as set forth in claim 1 in whichsaid second vapor-liquid lift pump is heat conductively connected tosaid first vapor-liquid lift pump.

3. An absorption refrigeration system as set forth in claim 1 in whichsaid vapor-expulsion unit comprises said first vaporliquid lift pump anda member for holding a body of absorption liquid, said secondvapor-liquid lift pump being heat conductively connected to said member.

4. An absorption refrigeration system as set forth in claim 1 whichincludes means for separating the raised liquid and lifting vaporpassing from an upper portion of said third conduit means and conductingthe separated vapor to said condenser and conducting the raised liquidto said higher temperature cooling element.

5. An absorption refrigeration system as set forth in claim I in whichsaid absorption liquid circuit includes said vapor-expulsion unit and anabsorber, the absorption liquid normally circulating through and betweensaid unit and said absorber,

and means for separating the raised liquid and lifting vapor passingfrom an upper portion of said third conduit means and conducting theseparated vapor to said higher temperature cooling element andconducting the raised liquid to said absorber.

6. An absorption refrigeration system as set forth in claim 1 in whichsaid absorption liquid circuit includes said vapor-explusion unit and anabsorber and a vessel disposed therebetween which is divided by apartition into first and second spaces for holding two bodies of liquidin communication with one another beneath their liquid surface levels,the first space having an inlet and outlet and forming a part of thepath of flow of absorption liquid from said absorber to saidvapor-expulsion unit, conduit means for conducting refrigerant fluidfrom said evaporator structure to the second space, and said secondconduit means conducting absorption liquid downward to said second pumpfrom the second space of said vessel at a level thereof which functionsas said one part of said absorption liquid circuit and at which regionthe absorption liquid has a higher concentration of refrigerant than inother parts of the absorption liquid circuit.

1. An absorption refrigeration system of the inert gas type comprising:a. a plurality of interconnected components; b. an absorption liquidcircuit comprising a plurality of said components including avapor-expulsion unit with a heat receiving part from which heat isderived for expelling refrigerant vapor from absorption liquid; c. asource of heat external to the system for heating said heat receivingpart; d. said vapor expulsion unit including a first pump for liftingliquid by vapor-liquid lift action to effect normal circulation ofabsorption liquid in its circuit during operation of the system; e. saidcomponents further including a condenser and cooling structure havinglow and higher temperature cooling elements; f. first conduit meansincluding said condenser for conducting refrigerant fluid from saidvapor-expulsion unit to said cooling structure; g. control meansincluding a thermostat affected by the temperature of said highertemperature cooling element for controlling said source of heat tosupply heat to said heat receiving part at a rate which will render saidfirst pump operable to raise liquid by vapor-liquid lift action tonormally circulate absorption liquid in its circuit during operation ofthe system or to substantially stop the supply of heat from said heatsource to said heat receiving part to render said first pumpsubstantially ineffective to raise liquid by vapor-liquid lift actionand substantially stop the normal circulation of absorption liquid inits circuit; h. said absorption liquid circuit having at least one partat a level which is normally free of liquid and above the liquid leveltherein when normal circulation of absorption liquid is effected duringopeRation of the system and below the liquid level in said circuit whenthe normal circulation of absorption liquid has substantially stoppeddue to said first pump being substantially ineffective to raise liquidby vapor-liquid lift action; i. a second pump for lifting liquid byvapor-liquid lift action by heat derived from said heat receiving part;j. second conduit means forming a stationary component of said systemand providing a passageway for conducting liquid downward from said onepart to said second pump when said one part is below the liquid level insaid absorption liquid circuit; and k. third conduit means forconducting fluid from said second pump to said higher temperaturecooling element.
 2. An absorption refrigeration system as set forth inclaim 1 in which said second vapor-liquid lift pump is heat conductivelyconnected to said first vapor-liquid lift pump.
 3. An absorptionrefrigeration system as set forth in claim 1 in which saidvapor-expulsion unit comprises said first vapor-liquid lift pump and amember for holding a body of absorption liquid, said second vapor-liquidlift pump being heat conductively connected to said member.
 4. Anabsorption refrigeration system as set forth in claim 1 which includesmeans for separating the raised liquid and lifting vapor passing from anupper portion of said third conduit means and conducting the separatedvapor to said condenser and conducting the raised liquid to said highertemperature cooling element.
 5. An absorption refrigeration system asset forth in claim 1 in which said absorption liquid circuit includessaid vapor-expulsion unit and an absorber, the absorption liquidnormally circulating through and between said unit and said absorber,and means for separating the raised liquid and lifting vapor passingfrom an upper portion of said third conduit means and conducting theseparated vapor to said higher temperature cooling element andconducting the raised liquid to said absorber.
 6. An absorptionrefrigeration system as set forth in claim 1 in which said absorptionliquid circuit includes said vapor-explusion unit and an absorber and avessel disposed therebetween which is divided by a partition into firstand second spaces for holding two bodies of liquid in communication withone another beneath their liquid surface levels, the first space havingan inlet and outlet and forming a part of the path of flow of absorptionliquid from said absorber to said vapor-expulsion unit, conduit meansfor conducting refrigerant fluid from said evaporator structure to thesecond space, and said second conduit means conducting absorption liquiddownward to said second pump from the second space of said vessel at alevel thereof which functions as said one part of said absorption liquidcircuit and at which region the absorption liquid has a higherconcentration of refrigerant than in other parts of the absorptionliquid circuit.